The present invention relates generally to code division multiple access (CDMA) communication systems and, more particularly, to power control for CDMA communication systems.
Code division multiple access (CDMA) is a technique used in personal communication service (PCS) systems for permitting the simultaneous access by multiple wireless devices to a single uplink frequency channel of a base station. In CDMA, a digital signal located at a wireless device is multiplied at the wireless device by a unique code corresponding to that device, which spreads the digital signal over a greater bandwidth. For example, a 10 kHz signal may be multiplied by a code which effectively creates a 100 kHz spread signal.
The spread signal modulates a carrier frequency signal which is in the range of the uplink frequency channel. The modulated carrier is then transmitted from the wireless device to the base station. The base station receives a composite spread signal of all the modulated carrier frequency signals from all wireless devices transmitting at that point in time. The base station demodulates the composite spread signal and then partially despreads the demodulated signal using the same unique code used at a particular wireless device for spreading. The despread signal approximates the pre-spreading data signal for the particular wireless device.
Within a sector of a base station, the population of PCS users can be split into fixed and mobile wireless users. A fixed user is a user that stays in place or moves at a relatively low rate of speed such as when walking during a call. A mobile user is a user that moves at a relatively high rate of speed such as when traveling in a vehicle during a call. All users are located within a sector of the base station for wireless communication with the base station.
Typically, each user in the sector is allocated the same amount of power to communicate with the base station. The measure of power allocated to each user is defined as the ratio of energy per bit to the noise power spectral density (Eb/No). The Eb/No level for each user is measured at the base station. In the prior art, the Eb/No level is set at the same level for all users in the sector and is dictated by the needs of mobile users. Unfortunately, this leads to a waste of resources for fixed users whose Eb/No level may be lower.
In general, mobile users have a higher requirement for Eb/No than fixed users. The multipath and fading experienced by a fixed user is much less volatile than that experienced by a mobile user because the fixed user resides in a fixed location. Because of the less severe fading environment, less power is needed to overcome the less volatile fast and slow fades. As a result, a lower Eb/No level can maintain the quality of the signal. The industry usually accepts Eb/No levels of 4 decibels (dB) for fixed users and 7 dB for mobile users.
A lower Eb/No correlates to greater capacity. Thus, if fixed users are allocated a different Eb/No level than mobile users (i.e., approximately three decibels less), rather than have the same Eb/No level as in prior art systems, then optimal base station capacity can be maintained while maintaining the quality of service for both fixed and mobile users. Consequently, what is needed is a method and system which dynamically adjusts Eb/No levels as a function of the needs of the users.
Accordingly, it is an object of the present invention to provide a method and system for dynamically adjusting an Eb/No level for a sector of a base station as a function of the needs of the majority of users in the sector.
It is another object of the present invention to provide a method and system for dynamically adjusting Eb/No levels for a sector of a base station as a function of the needs of each class of users in the sector.
It is a further object of the present invention to provide a method and system for dynamically adjusting Eb/No levels for a sector of a base station as a function of the needs of each user in the sector.
In carrying out the above objects and other objects, the present invention provides a method for controlling transmitted power of wireless devices within a sector of a base station of a code division multiple access (CDMA) communication system. The method includes estimating rate of movement of a wireless device. The rate of movement of the wireless device is then compared to a given rate of movement threshold interval. The transmitted power of the wireless device is then set to a power level corresponding to the given rate of movement threshold interval if the rate of movement of the wireless device falls within the given rate of movement threshold interval.
Further, the present invention provides another method for controlling transmitted power of wireless devices in a CDMA communication system. This method includes estimating rate of movement of each of the wireless devices. An average rate of movement of all of the wireless devices over a given time period is then determined from the estimated rates of movement of each of the wireless devices. The average rate of movement of all of the wireless devices is then compared to a given rate of movement threshold. The transmitted power of all of the wireless devices is then set to a high power level if the average rate of movement of all of the wireless devices is greater than the given rate of movement threshold. Similarly, the transmitted power of all of the wireless devices is set to a low power level if the average rate of movement of all of the wireless devices is less than the given rate of movement threshold.
Still further, the present invention provides yet another method for controlling transmitted power of wireless devices in a CDMA communication system. This method includes estimating rate of movement of each of the wireless devices. The rate of movement of each of the wireless devices is then compared to a given rate of movement threshold. The transmitted power of a wireless device is then set to a high power level if the rate of movement of the wireless device is greater than the given rate of movement threshold. Similarly, the transmitted power of a wireless device is set to a low power level if the rate of movement of the wireless device is less than the given rate of movement threshold.
The advantages accruing to the present invention are numerous. For instance, by adjusting the transmitted power of the wireless devices as a function of their needs, optimal base station capacity and the quality of service for both fixed and mobile users are maintained.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.